The long-range research goals have remained basically the same for several years. We have continued the study of a variety of heterogeneous and homogeneous charge-transfer processes for the purpose of attaining an understanding of transfer mechanisms. These have, over the past several years, involved several types of homogeneous electron transfer reactions of species generated electrochemically and the reaction of these species with bioredox components. Major emphasis has been directed toward mechanism and kinetic investigations of homogeneous and heterogeneous electron transfer reactions involving enzymes and carriers of biological systems. An important part of our efforts have been the continued development of the theory and methodologies for new instrumental techniques for studying transient species, and their kinetics applicable to charge transfer process. For example, emphasis for several years has been devoted to spectroelectrochemistry at optically transparent electrodes. Using these electrodes, we have developed an indirect coulometric titration method for the accurate assessment of stoichiometry (n value) and energetics (Eo' values) of multiple redox component enzymes or mixtures of these enzymes and other redox carriers in the presence and absence of inhibitors. Recent attention has been to the chemical modification of conducting surfaces for catalyzing electron transfer to biological redox component.